Figure 1.

(a) Top (upper panel) and side (bottom panel) views of crystal structure of bulk NiX₂ (X = Cl, Br, I). (b) Super cell model with introduced fracture used to simulate the exfoliation procedure. (c) Cleavage energy E_cl as a function of the separation between two fractured parts. (d) Variation of relative energy with the 2D lattice constant for the monolayer of NiX₂. The energy of equilibrium state is set to 0. (e) NiX₂ monolayer. d₀ is the vertical distance between two halide atomic planes.